Allow filtering the search results to the users home storage

This is done by adding a

```xml
<d:eq>
    <d:prop>
        <oc:owner-id/>
    </d:prop>
    <d:literal>$userId</d:literal>
</d:eq>
```

clause to the search query.

Searching by `owner-id` can only be done with the current user id
and the comparison can not be inside a `<d:not>` or `<d:or>` statement

Signed-off-by: Robin Appelman <robin@icewind.nl>